1. Field of the Invention
The present invention relates to a laser sintering apparatus, and particularly to a laser sintering apparatus for forming a three-dimensional model comprising a powder sintered body obtained by exposing a powdered body with a continuously-driven or pulse-driven laser beam in a predetermined-wavelength region that includes ultraviolet and sintering the powdered body.
2. Description of the Related Art
As three-dimensional CAD (Computer Aided Design) systems have recently spread, rapid prototyping systems for forming three-dimensional models in accordance with three-dimensional CAD data generated in virtual space within computers have been used.
Among rapid prototyping systems, an optical forming system was developed and spread in the beginning. In the case of the optical forming system, a three-dimensional model is formed by slicing CAD data at predetermined intervals on a computer to generate a plurality of sets of cross-sectional data, scanning the surface of a liquid photo-curable resin with a laser beam in accordance with the sets of cross-sectional data to cure the resin into layers, and successively laminating the layers of cured resin. As an optical forming method, a free-liquid-level method is widely known in which liquid photo-curable resin is stored in an open-top vessel and layers of cured resin are laminated while a forming table, disposed near the surface of the liquid photo-curable resin, is caused to successively sink from the surface of the resin.
Conventionally, optical forming apparatuses used in the optical forming system have included an apparatus for performing scanning with a laser plotter system and an apparatus for performing scanning with a movable mirror system, as described in an issue titled, Maruya, Yoji. 1992. Hikari zokei shisutemu no kiso, genjou, mondaiten. (Foundation, status quo, and issues in optical molding systems technology.) Kata Gijutsu (Die and Mold Technology)7, no.10:18-23.
FIG. 18 shows an optical forming apparatus according to the laser plotter system. In this apparatus, a laser beam emitted from a laser beam source 250 reaches an XY plotter 256 through an optical fiber 254 provided with a shutter 252 and is irradiated to a surface 266 of a liquid photo-curable resin 262 in a vessel 260 from the XY plotter 256. Furthermore, X- and Y-directional positions of the XY plotter 256 are controlled by a XY-positioning mechanism 258 provided with an X-positioning mechanism 258a and a Y-positioning mechanism 258b. Therefore, it is possible to cure the photo-curable resin 262 at predetermined positions of the surface 266 by turning a laser beam, irradiated from the XY plotter 256, on and off using the shutter 252 while moving the XY plotter 256 in the X and Y directions.
However, a forming apparatus according to the laser plotter system has a problem in that a shutter speed and a plotter moving speed are limited, and forming requires a long time.
FIG. 19 shows an optical forming apparatus according to the movable mirror system using a conventional galvanometer mirror. In this apparatus, a laser beam 270 is reflected from an X-axis rotation mirror 272 and a Y-axis rotation mirror 274 and irradiated to the photo-curable resin 262. The X-axis rotation mirror 272 controls an X-directional irradiation position by rotating about a Z-axis and the Y-axis rotation mirror 274 controls a Y-directional irradiation position by rotating about the X-axis. In the case of the movable mirror system, it is possible to increase a scanning speed compared to the case of the layer plotter system.
However, even in the case of the optical forming apparatus according to the movable mirror system, it takes 8 to 24 hours to form a three dimensional model of about 10 cm3, even when performing high-speed scanning at a rate of, for example, 2 to 12 m/s, because scanning is performed with a very small laser spot. Therefore, forming requires a long time. Moreover, the irradiation region of the laser beam 270 is limited because the laser beam 270 is reflected only when it is incident upon the Y-axis rotation mirror 274 at an angle within a predetermined range. Further, when the Y-axis rotation mirror 274 is disposed at a high position further away from the photo-curable resin 262 in order to widen an irradiation region, problems occur in that the diameter of a laser spot increases and, positioning accuracy and forming accuracy are thereby deteriorated. Positioning accuracy is also deteriorated if a rotation angle of the Y-axis rotation mirror 274 is increased, and the number of pincushion errors increases even though an irradiation range is increased. Moreover, an optical forming apparatus using a galvanometer mirror has problems in that adjustment of an optical system, such as adjustment of an optical axis and correction of distortion, is complex and a size of the apparatus is increased because the optical system thereof is complex.
Furthermore, regardless of the system used in an optical forming apparatus, a high-output ultraviolet laser-beam source is used as a laser-beam source, and a gas laser, such as an argon laser, has generally been used so far. Maintenance of gas lasers, however, such as injection of gas, is troublesome, and moreover, gas lasers are expensive. Therefore, when a gas laser is used, the price of an optical forming apparatus is raised, and the apparatus is increased in size because accessories including a cooling chiller are necessary. In view of this problem, Japanese Patent Application Laid-open (JP-A) No. 11-138645 discloses an optical forming apparatus provided with a plurality of light sources, each capable of irradiating an exposure region with a spot larger than a single pixel in order to conduct multiple exposure of pixels using the plurality of light sources. This apparatus can use inexpensive light-emitting diodes (LED) as the light sources because multiple exposure of pixels is carried out by the plurality of light sources, and it is unnecessary to use light sources that each have a large output.
The optical forming apparatus disclosed in JP-A No. 11-138645 has problems in that it cannot be used for highly detailed forming because the spot size of each light source is larger than a single pixel, many unnecessary operations are performed because multiple exposure of pixels is carried out with the plurality of light sources, and forming requires a long time. Also, the optical forming apparatus has problems in that a size of an exposure portion is increased due to increasing the number of the light sources. Moreover, even when multiple exposure of pixels is carried out with the luminous energy outputted by the LEDs, there is a possibility that sufficient resolution may not be obtained.
A powder laser sintering apparatus, developed subsequent to optical forming apparatuses that use a photo-curable resin, is known among rapid prototyping systems, which are widely used at present. The powder laser sintering apparatus scans the surface of a powdered body with a laser beam in accordance with cross-sectional data of a three-dimensional model generated on a computer. Processing for curing the powdered body, including gradually melting and sintering the powdered body by scanning with laser light, is repeated. A three-dimensional model made of a laminated powdered sintered body is then formed due to the repetition of the processing.
The powder laser sintering apparatus has advantages in that various materials can be selected and it can directly manufacture not only function-evaluation models of superior toughness and precise cast patterns and dies, but also metallic molds and metallic parts, and it has a wide range of applications. Moreover, the laser sintering apparatus is less expensive than an optical forming apparatus and has a high forming speed. Therefore, its use for confirmation of design models is becoming more and more entrenched. However, because the powder laser sintering apparatus also uses a movable mirror system, such as a galvanometer mirror system, and a gas laser or a solid-state laser, such as a CO2 laser (having a wavelength of 10.6 xcexcm) or a YAG laser (having a wavelength of 1.06 xcexcm), which output high-output infrared rays, as light sources, the apparatus has the same problems as the above-described optical forming apparatus.
The present invention has been achieved in order to solve the above-described problems of prior art, and an object thereof is to provide a laser sintering apparatus capable of realizing high-speed and highly detailed forming. Another object of the invention is to provide an inexpensive, high-speed, and highly precise laser sintering apparatus.
To achieve the above objects, the invention uses a laser sintering apparatus for forming a three-dimensional model by exposing a powdered body with a continuously-driven or pulse-driven laser beam in a predetermined wavelength region that includes ultraviolet, comprising an exposure component for exposing predetermined regions corresponding to a plurality of pixels on the surface of the powdered body with a continuously- or pulse-driven laser beam in a predetermined wavelength region including ultraviolet modulated every pixel correspondingly to the image data emitted from a light source and a moving component for moving the exposure component relatively to the surface of the powdered body.
By using a laser beam in a predetermined wavelength region including ultraviolet, it is possible to greatly increase a light absorption rate for a powdered body compared with the case of using a laser beam in an infrared wavelength region. Particularly, when a powdered body is made of a metal, the light absorption rate is greatly increased. Because a laser beam in a predetermined wavelength region including ultraviolet has a short wavelength, it has a large photon energy and thereby, it is easy to convert the laser beam into sintering energy for sintering a powdered body. Thus, because a laser beam in a predetermined wavelength region including ultraviolet has a large light absorption rate and it can be easily converted into sintering energy, it is possible to sinter a powdered body at a high speed. Moreover, the laser beam has a short wavelength, it is possible to condense the laser beam like a very small spot or thin line (such as 0.4 xcexcm though the spot of a CO2 laser is 10.6 xcexcm), and it is possible to perform sintering very minutely.
Moreover, by exposing a powdered body with a pulse-driven laser beam, diffusion of heat produced due to irradiated light is prevented. Therefore, light energy is effectively used to sinter a powdered body and high-speed forming is realized. Moreover, heat diffusion is prevented, a powdered body is sintered at a size almost equal to the shape of an irradiated beam and very-minute forming at a smooth surface is realized. Therefore, it is preferable that a pulse-driven laser beam has a smaller pulse width. That is, a pulse width ranges preferably between 1 psec to 100 nsec and more preferably 1 psec to 300 psec. It is preferable that a predetermined wavelength region including ultraviolet ranges between 350 to 420 nm and the highest output can be expected for a wavelength of 405 nm as a predetermined wavelength region including ultraviolet because of using a GaN-based semiconductor laser at a lower cost.
In the case of the laser sintering apparatus, an exposure component exposes predetermined regions corresponding to a plurality of pixels on the surface of a powdered body with a continuously- or pulse-driven laser beam in a predetermined wavelength region including ultraviolet modulated every pixel correspondingly to the image data emitted from a light source. Therefore, it is possible to simultaneously sinter and cure predetermined regions corresponding to a plurality of pixels on the surface of the powdered body and thus realize very-minute forming. Moreover, because a moving component can move the exposure component relatively to the surface of the powdered body, it is possible to restrict the area of the predetermined regions to be simultaneously exposed by the exposure component, improve a spatial resolution, and realize very-minute forming.
In the case of the above laser sintering apparatus, it is possible to further increase the forming speed by using a plurality of exposure components and making each of the exposure components independently relatively movable to the surface of a powdered body.
An exposure component can be constituted by a light source and a spatial light modulator for modulating a continuously- or pulse-driven laser beam in a predetermined wavelength region including ultraviolet emitted from the light source every pixel in accordance with image data. The spatial light modulator can be constituted by, for example, a digital micromirror device or a grating light valve (GLV). Details of the GLV are described in the U.S. Pat. No. 5,311,360.
It is also allowed to constitute a laser sintering apparatus of the invention so as to be provided with an exposure component having a scanning function for scanning and exposing predetermined regions including a plurality of pixels for the image data on the surface of a powdered body with a laser beam in a predetermined wavelength region including ultraviolet modulated every pixel correspondingly to image data emitted from a light source and a moving component for moving the exposure component relatively to the surface of the powdered body. Because the laser sintering apparatus is provided with a scanning function for scanning and exposing predetermined regions including a plurality of pixels for the image data on the surface of a powdered body with a laser beam in a predetermined wavelength region including ultraviolet modulated every pixel correspondingly to the image data emitted from a light source, high-speed very-minute forming can be realized.
For example, it is allowed to constitute an exposure component by a light source and a space-modulation-device array in which spatial light modulators for respectively modulating a continuously- or pulse-driven laser beam in a predetermined wavelength region including ultraviolet emitted from the light source every pixel in accordance with image data in a first scanning direction (e.g. main scanning direction). In this case, a moving component moves the exposure component relatively to the surface of a powdered body so that the space-modulation-device array moves in a second scanning direction (e.g. subscanning direction) crossing the first scanning direction. Moreover, it is allowed that the space-modulation-device array scans in the main scanning direction and a movable mirror (scanner mirror) performs exposure in the subscanning direction. It is possible to use a digital micromirror device (DMD) in which linear grating light valves and micromirrors are linearly arranged as a spatial light modulator constituting the above space-modulation-device array.
A laser sintering apparatus of the invention is a laser sintering apparatus for forming a three-dimensional model by exposing a powdered body with a continuously- or pulse-driven laser beam in a predetermined wavelength region including ultraviolet. Moreover, it is allowed that the laser sintering apparatus is a laser sintering apparatus comprising an exposure component in which a plurality of exposure units for scanning and exposing predetermined regions corresponding to a plurality of pixels on the surface of a powdered body with a continuously- or pulse-driven laser beam in a predetermined wavelength region including ultraviolet modulated every pixel correspondingly to image data emitted from a light source are arranged like an array.
The above laser sintering apparatus realizes high-speed very-minute forming because the exposure units arranged on the exposure component like an array scan and expose regions corresponding to a plurality of pixels on the surface of a powdered body with a continuously- or pulse-driven laser beam in a predetermined wavelength region including ultraviolet modulated every pixel in accordance with image data emitted from a light source.
In the case of the above laser sintering apparatus, the above exposure units can be respectively constituted by including a light source, a condensing optical system for condensing a continuously- or pulse-driven laser beam in a predetermined wavelength region including ultraviolet emitted from the light source, and a deflection device for modulating the continuously- or pulse-driven laser beam in the predetermined wavelength region including ultraviolet condensed by the condensing optical system every pixel in accordance with image data. Because each of the exposure units is downsized compared to a case of using a conventional paired movable mirrors by using a modulating deflection device for each pixel in accordance with image data. Therefore, it is possible to arrange many exposure units on an exposure component and moreover, realize high-speed very-minute forming, and decrease an exposure region per exposure unit. Therefore, it is possible to eliminate most pincushion errors. Moreover, each of the exposure unit can be constituted so that a light source, a condensing optical system, and a deflection device are sealed in a package. The deflection device can use a two-dimensional microscanner.
The light source can use the following light source for emitting a continuously- or pulse-driven laser beam in a predetermined wavelength region including ultraviolet. The light absorption rate of a powdered body (particularly, a metallic powdered body) to a laser beam in a predetermined wavelength region including ultraviolet is very high compared to a conventional light absorption rate to infrared light. Moreover, because the wavelength of a laser beam in a predetermined wavelength region including ultraviolet is very small compared to that of infrared light, it is possible to condense the laser beam at a very small spot. As a result, high-speed exposure can be made even with an output smaller than a laser output used for a conventional powdered body. Therefore, by using a laser beam in a predetermined wavelength region including ultraviolet, it is possible to perform high-speed very-minute laser sintering compared to a case of using infrared light. Moreover, by using a pulse-driven laser beam in a predetermined wavelength region including ultraviolet, heat diffusion is prevented and thereby high-speed very-minute forming is realized. That is, by using continuously or pulse-driven laser beam in a predetermined region including ultraviolet as a light source, it is unnecessary to use an expensive gas laser or solid-state laser and it is possible to provide a high-speed very-minute laser sintering apparatus.
(1) Gallium-nitride-based-semiconductor laser. For example, it is allowed to use a gallium-nitride-based-semiconductor laser having a broad-area light-emitting region, a semiconductor laser having a 10 mm-long bar-type structure, or a semiconductor laser constituted by a gallium-nitride-based semiconductor-laser chip having a plurality of light-emitting points. Moreover, by using an array-type semiconductor laser constituted by mounting a plurality of gallium-nitride-based semiconductor-laser chips respectively having a plurality of light-emitting points, it is possible to obtain a higher output.
(2) Semiconductor-laser-exciting solid-state laser for emitting a laser beam obtained by exciting solid-state-laser crystal by a gallium-nitride-based-semiconductor laser by wavelength-converting the laser beam by a light-wavelength conversion device. For example, it is allowed to use solid-state laser crystal to which at least Pr3+ is added as a rare earth element, a gallium-nitride-based-semiconductor laser for emitting a laser beam for exciting the solid-state-laser crystal, or a semiconductor-laser-exciting solid-state laser provided with a light-wavelength conversion device for light-wavelength-converting a laser beam obtained by exciting the solid-state-laser crystal into the light in an ultraviolet region.
The solid-state-laser crystal to which Pr3+ is added is excited by a GaN-based semiconductor laser and effectively oscillated in a wavelength band of 700 to 800 nm. That is, because a solid-state laser beam in an infrared region at a wavelength of 720 nm which is an oscillation line of Pr3+ is efficiently oscillated in accordance with transition of, for example, 3P0xe2x86x923F4, it is possible to obtain high-intensity ultraviolet light at a wavelength of 360 nm by wavelength-converting the solid-state laser beam into second harmonic by a light-wavelength conversion device. Moreover, a low-cost laser-exciting solid-state laser is realized without complicating a configuration like a case of generating third harmonic.
(3) Fiber laser for emitting a laser beam obtained by exciting a fiber by a gallium-nitride-based-semiconductor laser by light-wavelength-converting the laser beam by a light-wavelength conversion device. For example, it is allowed to use a fiber having a core jointly doped with at least one of Er3+, Ho3+, Dy3+, Eu3+, Sn3+, Sm3+, and Nd3+ on one hand and Pr3+ on the other, a gallium-nitride-based-semiconductor laser for emitting a laser beam for exciting the fiber, or a fiber laser provided with a light-wavelength conversion device for wavelength-converting a laser beam obtained by exciting the fiber.
Er3+, Ho3+ Dy3+, Eu3+, Sn3+, Sm3+, and Nd3+ respectively have an absorption band in a wavelength of 380 to 430 nm, which can be excited by a GaN-based semiconductor laser. Moreover, by energy-moving excited electrons to the exciting level of Pr3+ (e.g. 3P0xe2x86x923F1) and dropping the electrons to a lower level, it is possible to oscillate blue, green, and red regions which are oscillation lines of Pr3+. The wavelength of 380 to 430 nm is a wavelength band that is comparatively easily oscillated by a GaN-based semiconductor laser. Particularly, a wavelength of 400 to 410 nm is a wavelength band from which the maximum output of a GaN-based semiconductor laser can be obtained. Therefore, by exciting Er3+, Ho3+, Dy3+, Eu3+, Sn3+, Sm3+, and Nd3+ by a GaN-based semiconductor laser, the absorption quantity of excited light increases and high efficiency and high output are achieved. Moreover, a concise configuration requiring less optical components is obtained, losses are reduced, and a temperature stabilization region is widened.
It is possible to use not only the single length and breadth mode type as a GaN-based semiconductor laser serving as an exciting light source but also the broad-area type, phased-array type, and MOPA type, or one or more fiber-type high-output types obtained by multiplexing a GaN-based semiconductor laser and connecting with a fiber. Moreover, it is possible to use a fiber laser as an exciting light source. Thus, by using a high-output exciting light source, it is possible to obtain a higher output such as a W (watt)-class high output. Furthermore, a laser using Pr3+ having a wide emission spectrum, as mentioned in (2), (3), can be easily psec-pulse-driven by mode locking and can be repetitively operated. Furthermore, because of psec oscillation, high-efficiency wavelength conversion is realized.
(4) Fiber laser or fiber amplifier for emitting a laser beam obtained by exciting a fiber by a semiconductor laser for emitting the light in an infrared region by wavelength-converting the laser beam by a light-wavelength conversion device. For example, it is allowed to use a fiber having a core doped with Nd3+ or Yb3+ or both Er3+ and Yb3+, a semiconductor laser for emitting a laser beam in an infrared region for exciting the fiber, or a fiber laser or fiber amplifier provided with a light-wavelength conversion device for wavelength-converting a laser beam obtained by exciting the fiber into light in an ultraviolet region. The light-wavelength conversion device can use a THG (third-harmonic-generation) device or an FHG (fourth-harmonic-generation) device.
By using a fiber laser, it is possible to improve the mode matching between exciting light and an oscillation beam for a conventional solid-state laser. Therefore, it is possible to realize a high efficiency. Moreover, in the case of a fiber laser system, it is possible to stably constitute a mode-locking mechanism for a conventional solid-state laser at a low cost, make the oscillation spectrum of the above fiber laser broad, and perform short-pulse driving (psec) and a high repetitive operation (100 MHz). As a result, it is possible to obtain THG light and FHG light according to wavelength conversion at a high efficiency.
Moreover, in the case of a fiber amplifier, by using LD light which can be repeatedly used many times and made short-pulse as a main light source, it is possible to realize a high output by the fiber amplifier and obtain THG light and FHG light according to wavelength conversion at a high efficiency. Thus, it is possible to obtain a high-output and high-repetitive ultraviolet laser beam for a conventional solid-state laser. As a result, a low-cost light source suitable for high-speed exposure is obtained.
(5) Laser obtained by multiplexing a gallium-nitride-based-semiconductor laser to a fiber. For example, it is possible to obtain a high output from a fiber by multiplexing and combining a plurality of gallium-nitride-based-semiconductor lasers with a multiplexing optical system. It is also allowed to use a laser obtained by multiplexing a semiconductor laser using a semiconductor laser chip for emitting a plurality of beams into a fiber with a condensing optical system. Moreover, it is allowed to multiplex a gallium-nitride-based-semiconductor laser beam having a broad-area light-emitting region into a fiber. By arranging these fibers like an array and using the array as a linear light source or arranging them like a bundle and using the bundle as a flat light source, it is possible to obtain a higher output.
(6) Moreover, it is allowed to constitute a light source by including a plurality of laser beam sources and a multiplexing optical system for multiplexing laser beams emitted from the laser beam sources. As the above laser beam source, it is possible to use any one of the laser beam sources in the above Items (1) to (5). It is possible to raise the output of the laser beam source by using the multiplexing optical system and thereby multiplexing the laser beams emitted from the laser beam sources.
Moreover, the above-described former laser beam source can not only realize a tens-of-Ws-class output that has not been ever used but also realize short-pulse oscillation at psec order and high-speed very-minute exposure.
Particularly, because a gallium-nitride-based-semiconductor laser is a semiconductor laser, it is possible to constitute the laser as a low-cost system. Moreover, because a gallium-nitride-based-semiconductor laser has a very small mobility of transfer and a very-large thermal conductance, it has a very high COD (Catastrophic Optical Damage) value compared to a light source in an infrared wavelength region. Moreover, because the laser is a semiconductor laser, it allows repetitive operations in accordance with pulses having a high peak power in a short cycle. Therefore, a gallium-nitride-based-semiconductor laser is a light source well suited for an inexpensive high-speed very-minute laser sintering apparatus.
A laser sintering apparatus of the invention has an advantage that high-speed and very-minute forming can be realized. Moreover, an exposure unit of the invention is decreased in size compared to a conventional one. Therefore, an advantage can be obtained that it is possible to arrange many exposure units. Moreover, when using a predetermined laser beam source as a light source, advantages are obtained that it is possible to provide an inexpensive high-speed and very-minute laser sintering apparatus and an exposure unit.